FIG. 23 schematically shows the structure of an image recording unit of a general ink-jet recording apparatus.
The ink-jet recording apparatus includes a recording head 201. A number of nozzles are arranged side by side in a certain recording head 201. A recording medium 202 (such as recording sheet) on which an image is to be recorded is conveyed to below the recording head 201. The recording head 201 is moved in a direction orthogonal to a conveying direction 203 of the recording sheet 202, i.e., in a direction (main scanning direction) perpendicular to the sheet in this drawing. The recording head 201 ejects ink from the nozzles with predetermined timing while being moved. Thereby, an image is recorded on the recording sheet 202.
Recently, some ink-jet recording apparatus have a function to record an image on the recording sheet 202 like, for example, photographic printing. Such image recording is performed without providing a margin to an edge of the recording sheet 202, and is called what is called “borderless recording.” When the borderless recording is performed, it is necessary to correctly maintain the distance between an edge of the recording sheet 202 and the recording head 201. Therefore, the platen 204 includes a movable rib 206 that slides in the conveying direction 203 in addition to fixed ribs 205. The movable rib 206 supports the recording sheet 202 from below, and follows the recording sheet 202 conveyed during image recording.
FIGS. 24A to 24C and FIGS. 25A to 25C schematically show the operation of sliding of the movable rib 206 in the conventional ink-jet recording apparatus.
As shown in FIG. 24A, the movable rib 206 slides to the upstream side in the conveying direction from the middle of the platen 204 in response to the conveyance of the recording sheet 202. That is, the movable rib 206 meets to support the leading edge of the recording sheet 202. The movable rib 206 slides to the position of an upstream end in the conveying direction as shown in FIG. 24B, and thereafter, slides to downstream side in the conveying direction as shown in FIG. 24C. That is, the movable rib 206 slides so as to follow the conveyance of the recording sheet 202 while supporting the recording sheet 202. This keeps the distance between the recording sheet 202 and the recording head 201 constant. Such ink-jet recording apparatus is disclosed in, for example, JP-A-2006-326990.
The movable rib 206 is slid in synchronization with the conveyance of the recording sheet 202 by a required sliding mechanism. However, the movable rib 206 may not be slid in synchronization with the conveyance of the recording sheet 202 due to mechanical errors or other factors of the sliding mechanism or a conveyor mechanism of the recording sheet 202. For example, in FIGS. 24A to 24C, the sliding initiation of the movable rib 206 is relatively too earlier than the conveyance of the recording sheet 202. Accordingly, the return of the movable rib 206 becomes too early, and the movable rib 206 will support the leading edge of the recording sheet 202. Therefore, when the recording head 201 begins to eject ink (see FIG. 24C), the ink adheres to a downstream portion of the movable rib 206 in the conveying direction. The ink adhering to the movable rib 206 may spread to the upper end of the movable rib 206, thereby soiling the recording sheet 202.
Further, in FIGS. 25A to 25C, the sliding initiation of the movable rib 206 is relatively too later than the conveyance of the recording sheet 202. Accordingly, when the recording head 201 begins to eject ink (see FIG. 25B), the movable rib 206 cannot support the recording sheet 202. Therefore, the ink adheres to the upper end of the movable rib 206, and the downstream portion thereof in the conveying direction. Moreover, as shown in FIG. 25C, the movable rib 206 returns after it has further slid to the upstream side in the conveying direction. Therefore, the ink adhering to the movable rib 206 will soil the rear surface of the recording sheet 202 severely.
Therefore, it is preferable that the position of a leading edge of the recording sheet 202 conveyed is sensed correctly, and sliding of the movable rib 206 is controlled on the basis of the position of the recording sheet 202. However, in order to realize such control, as well as a sensor that senses the position of a leading edge of the recording sheet 202 is specially needed, the sliding mechanism of the movable rib 206 also becomes complicated. This results in increased size and cost of an ink-jet recording apparatus.
In order to realize prevention of soiling of the movable rib 206 and the recording sheet 202 without adding a new sensor, etc., there may be provide means for adjusting the timing of sliding initiation of the movable rib 206 in view of a deviation in conveyance of a recording sheet. That is, assuming that the conveyance of the recording sheet 202 becomes relatively early, the timing of sliding of the movable rib 206 is advanced. Further, assuming that the conveyance of the recording sheet 202 becomes relatively late, the timing of sliding of the movable rib 206 is delayed.
However, for example, when the timing of movement initiation of the movable rib 206 is set to become late, actually, delay may not occur in conveyance of the recording sheet 202, or the conveyance of the recording sheet 202 may not become early. This is the same situation as a case where the timing of sliding of the movable rib 206 becomes relatively earlier than the timing of conveyance of the recording sheet 202. Therefore, when the recording head 201 begins to eject ink (refer FIG. 25B) as mentioned above, the movable rib 206 will not be able to support the recording sheet 202, but ink may adhere to the upper end of the movable rib 206 and the downstream portion thereof in the conveying direction. Accordingly, it is not possible to cope with a deviation in the conveying timing of the recording sheet 202 only by adjustment of the sliding initiation timing of the movable rib 206.